This application claims the benefit of Korean Patent Application No. P1999-33979, filed in Korea on Aug. 17, 1999, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a charge coupled device, and more particularly, to a charge coupled device having a charge transmission portion that is divided into a plurality of regions, each of these regions having a respective voltage difference, for improving a charge transmission efficiency of the device.
2. Discussion of the Related Art
A related art charge coupled device will be explained with reference to the attached drawings. FIG. 1 illustrates a plan view of a related art solid state image sensor, and FIG. 2 illustrates a plan view of a related art horizontal charge coupled device.
Referring to FIG. 1, an image sensor arrangement is illustrated including a charge coupled device for converting a signal of light into an electrical signal. The image sensor arrangement includes a plurality of photoelectric conversion regions 11 for effectuating photo-electric conversion and accumulation of generated charges. The photoelectric conversion regions, are preferably photodiode regions. The image sensor arrangement also includes a charge transmission channel comprised of Vertical Charge Coupled Devices (VCCDs) 12a and a Horizontal Charge Coupled Device (HCCD) 12b for transmission of signal charges generated in the photodiode regions 11. The image sensor arrangement also includes a sense amplifier 13 for sensing the signal charge transmitted through the charge transmission channel. The charge transmission channel is provided with the VCCDs 12a for transmission, in a vertical direction, of charges generated in a plurality of photodiode regions 11. The HCCD 12b is provided coupled to the VCCDs for transmission of the charges that were transmitted in the vertical direction in the VCCDs in a horizontal direction.
Referring to FIG. 2, the HCCD portion of the charge transmission channel is provided with a channel region 21 formed by implanting ions, such as xe2x80x98Asxe2x80x99, in a xe2x80x98pxe2x80x99 type well formed in a surface of a semiconductor substrate. A plurality of gate electrodes 22 are formed on the channel region 21 separated from each other in sequence, as illustrated at least in FIG. 2, for transmission of charges.
The charge transmission of the foregoing charge transmission channel is formed in the following way. FIGS. 3A and 3B illustrate sections across lines A-Axe2x80x2 and B-Bxe2x80x2 in FIG. 2. The channel region 21 has a uniform concentration as well as a uniform potential distribution in a state where no clock signal is provided to the gate electrodes 22. The HCCD is formed by implanting xe2x80x98pxe2x80x99 type impurity ions in the semiconductor substrate N-SUB uniformly, to form a xe2x80x98pxe2x80x99 type well, and implanting xe2x80x98nxe2x80x99 type impurities in the xe2x80x98pxe2x80x99 type well region uniformly. When clock signals having supply level differences are provided to the gate electrodes 22 on the HCCD of the charge coupled device, potential differences are caused by these supply level differences.
These potential differences cause the charges to move in one direction within the HCCD. In this instance, the charge signal moves through the channel region 21 of the HCCD distributed uniformly throughout the entire channel region 21 regardless of the intensity of the charge signal. Since the HCCD should preferably receive and read all the charges transmitted from the VCCDs within a short time period, the HCCD operates using two phase clocking while the VCCDs operate using four phase clocking. While this related art CCD performs relatively efficiently when the amount of charge moving through the channel region is large, its performance decreases significantly when the amount of charge moving through the channel region is small. There are at least three reasons for this.
First, the movement of charges distributed throughout the channel region 21 under the gate electrodes 22 may cause a small charge amount to be lost due to a defective channel region. Secondly, when a small charge amount moves through the relatively wide channel region of the HCCD, the potential of the charge may not be sustained, and may be lost as a result of the voltage applied to the gate electrodes. Third, while a narrow channel region is favorable for a high charge transmission efficiency for reasons discussed above, the width of the HCCD needs to wide enough to be compatible with a possible maximum charge amount However, such a width can drop the charge transmission efficiency of the HCCD when small charges are transmitted, as discussed above.
Accordingly, the present invention is directed to a charge coupled device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a charge coupled device which has a high charge transmission efficiency, with either a large or small amount of transmitted charges.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the charge coupled device includes a plurality of photoelectric conversion regions; a plurality of vertical charge coupled devices (VCCDs) provided between the photoelectric conversion regions for transmission of charges generated at the photoelectric conversion regions in a first direction; and a horizontal charge coupled device (HCCD) coupled to the VCCDs and having a channel region including a plurality of channels for transmission of the charges previously transmitted through the VCCDs in a second direction. The channel region is formed such that one of the plurality of channels has a higher potential than the remaining channels. The remaining channels have potentials that gradually become lower than the highest potential moving in a direction away from the channel with the highest potential. The channel region transmits the charges within the HCCD so that the charges are gathered together centered around the channel having the highest potential during transmission of the charges.
In another aspect, a charge coupled device includes a semiconductor substrate; photoelectric conversion regions formed in a well region in a surface of the semiconductor substrate; vertical charge coupled devices (VCCDS) for transmission of charges generated at the photoelectric conversion regions in a first direction; and a horizontal charge coupled device (HCCD) for transmission of the charges previously transmitted through the VCCDS in a second direction. The HCCD is formed in a well region that is separated into a plurality of split portions.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.